Booster Battery Drain & horn buzz.

[550Anniv]

Hi Folks. I have a 2004 Boxster, and have just replaced the battery as it was very old and I
Had noticed the cranking speed a little lazy.
However, I noticed a very very faint buzz from the alarm horn on the right hand side of the battery.
When the horn is disconnect the buzzing disappears.
So, thinking I have an issue, I borrowed a 'D Clamp' to see if I have a electrical discharge.
With the key removed, car not locked and left for 2 hours to enable everything to go to sleep
I get a discharge of 0.17 amps (if I read the display correctly)
If I disconnect or connect the very slightly buzzing alarm horn it makes no difference to the
Discharge.
I have pulled all the fuses one by one, but the discharge doesn't really ulter.

Can anyone confirm what is an acceptable discharge as I cannot find what the correct spec
Should be.... Or any pointers why my alarm horn makes a constant very faint buzz??